1. Field of the Invention
This invention relates generally to rubber curing and more specifically, to curing of rubber articles.
2. Description of the Related Art
When tires become worn, they can be restored with new tread. Large truck tires and bus tires, for example, are typically retreaded as part of a routine tire-management program. The carcass of a these types of tires is expected to last several hundred thousand miles and be amenable to having a new tread adhered to it several times. Such tires are quite expensive and are therefore bought with the expectation that their high initial costs are offset by the long service life of the carcass and the low comparative cost of retreading. Indeed, the economics included in the selection and purchase of such tires often dictate that the original tires be capable of being retreaded as many as three or four times.
A variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove remaining tread material from the tire carcass, for example, by a procedure known as buffing. Next a layer of green (uncured) rubber, known as “cushion gum,” may be applied to the carcass. This layer of extruded uncured rubber may be stitched or adhesively bonded to the carcass. Next, a tread band is applied atop the layer of cushion gum. In the cold recapping process, the tread is cured rubber, and has a tread pattern already impressed in its outer surface. The tire is then placed in an autoclave, and heated under pressure for an appropriate time to induce curing of the gum layer, and bonding of the gum layer to the tread and the carcass. In the hot recapping process, the tread is uncured rubber, and has no tread pattern. The tire is then placed in a tire mold and heated under pressure for an appropriate time to cure the gum layer and the tread, and to cause the gum layer to bind with the tread and the carcass. The term “cure” refers to the formation of cross-links between the elastomer molecules in the rubber compound, otherwise known as vulcanization.